[Mesa-dev] [MR] mesa/i965: ARB_gl_spirv and ARB_spirv_extensions implementation, plus 4.6

[apinheiro]

https://gitlab.freedesktop.org/mesa/mesa/merge_requests/178

TL; DR; This series implements all the mesa bits needed to enable 
ARB_gl_spirv and ARB_spirv_extensions on the i965 driver, and with that, 
expose OpenGL 4.6 on that driver.

Detailed explanation: we reached a point where we consider our 
development branch good enough to enable both extensions on i965, so we 
preferred to send the full series, instead of keeping sending subseries 
of specific sub-features. As a collateral effect of enabling both 
extensions we can also expose OpenGL 4.6 on i965.

It is worth to note that some of those patches could be easily squashed 
with some others, but we preferred to keep them, to make easier the 
review process.

Although on this MR the patch numbering will get quickly obsolete, here 
an overview of the the patches at the moment this MR got sent:

  *

    Patches 1-5 provides improvements over current ARB_gl_spirv xfb
    support. It basically extends the xfb nir gathering pass recently
    added for Vulkan needs, and then replaces the ARB_gl_spirv custom
    one and uses it instead.

  *

    Patches 6-24 implemens UBO/SSBO support, and calls to link them on
    the i965 driver. It is worth to note that it is using the new deref
    based UBO/SSBO path, so we could get arrays of arrays properly
    supported on the spirv to nir pass.

  *

    Patches 25-33 adds the different resources already supported by the
    ARB_gl_spirv linker to the resource list (input/output, ubo/ssbo,
    etc), and fill up properly some data for such resources, in
    preparation to the program interface queries support.

  *

    Patches 34-41 fixes and extends several program interfaces queries.
    In most of the cases they are just to handling the fact that now
    resource name can be NULL, and applies the value expected for such
    case defined on the ARB_gl_spirv spec.

  *

    Patches 42-45 gets serialization working when using SPIR-V shaders.
    As the previous case, most patches are about handling the fact that
    names can be NULL, plus initializing UniformDataDefaults when using
    the ARB_gl_spirv nir linker. All this got interaction with
    ARB_get_program_binary working (at least with the tests we had an hand).

  *

    Patch 46 prevents to load the shader cache. Even if we handle the
    serialization with previous patches, shader cache is still not
    working with SPIR-V shaders, so we prevent the cache to be used on
    that case. Taking into account that the ARB_gl_spirv spec doesn't
    require the cache to be working, we thought that we shouldn't wait
    to enable the extension until finishing it, and clearly we shouldn't
    wait for it to send to review.

  *

    Patches 47-48 add some validations. It is worth to note that
    ARB_gl_spirv doesn't require too much validation. That includes the
    validations added with those patches. As with Vulkan, it is assumed
    that the SPIR-V shaders should be correct. Having said so, the spec
    also allows to raise them as link errors if you want. We implemented
    those validations during development, and we think that they are
    fine and simple enough validations to be included.

  *

    Patch 49: enable ARB_gl_spirv on i965.

  *

    Patches 50-55 adds the support for ARB_spirv_extensions, and enable
    it on i965. FWIW, we sent this several months ago to review. It
    didn't change anything since then (except minor changes due rebases).

  *

    Patch 56: exposes OpenGL 4.6 on i965.

So about how this series got tested. First, this series gets all the 
ARB_gl_spirv and ARB_spirv_extensions CTS tests passing. So in theory 
that should be enough to enable both extensions. In the practice, those 
tests were not enough, so we tested this series with piglit patches. For 
that we had two types of tests:

  *

    Barebone tests: tests we were adding as we implemented the
    extension. Piglit master already have some of them.

  *

    Borrowed tests: recycled tests from other specs. For this we use a
    heavily modified version of a script wrote by Nicolai Hähnle, that
    do some fixes on shader_test tests, and then uses glslang to convert
    them to SPIR-V.

Unfourtunately, right now the previous two are not ready for review 
(except those that we already sent), as we were focusing on getting the 
Mesa support done. We are cleaning both this week, so we will send to 
review all those on the following weeks.

Having said so, right now we get the following outcome when run all the 
shader piglit tests on SPIR-V mode:

[34596/34596] skip: 6020, pass: 28559, fail: 17, crash: 0

FWIW, this is the outcome on GLSL mode:

[34596/34596] skip: 4877, pass: 29714, fail: 3, crash: 2

Probably the main difference is the greater amount of skipped tests on 
the SPIR-V run (for example, those crashed tests on the GLSL run are 
skipped on the SPIR-V run). This increase comes from:

  *

    Tests that doesn't make sense on ARB_gl_spirv, like old GLSL
    functionality that is not supported, or name-based validations.

  *

    Glslang limitations when dealing with some shaders, usually when
    auto-assigning locations/bindings through stages. Note that for the
    latter, it is assumed that your GLSL shaders would set explicitly
    the location/bindings. glslang provide that functionality somewhat
    experimental, as a way to support already written old shaders (like
    we have).

For both we try to automatize the skipping as much as possible (on the 
mentioned script) but we also maintain a exclude list for them.

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